In such machines the forming of the blisters in the preheated and therefore readily deformable carrier strip is generally done with the aid of a source of compressed air driving portions of that strip into suitably shaped cavities or recesses of an underlying die whose bottoms are vented to the atmosphere. The die, serving as a movable mold plate, may be periodically reciprocated toward and away from a fixed abutment plate having air channels aligned with these cavities. After the deformed strip leaves the die, and upon sufficient hardening of the blisters, the latter may be engaged by stationary guides as well as by one or more peripherally indented transport rollers for advancing the strip in a precisely controlled manner through the filling and sealing stations following the molding station. After the filled blisters have been hermetically sealed by the application of the cover strip, the resulting composite tape may be divided at a cutting station into packages of one or more blisters each. The sealing station may include one or more counterrollers coacting with one of the aforementioned transport rollers to laminate the cover strip onto the underlying carrier strip, with or without the application of additional heat.
In a packaging machine of this type it is desirable to monitor the contents of cells--not necessarily formed as blisters--downstream of the filling station and to eliminate defective packages leaving the cutting station. When the carrier strip formed with the cells is of light-transmissive material, i.e. transparent or translucent, such monitoring can be conveniently performed by a photoelectric sensor. If the cover strip subsequently sealing the cells is not sufficiently light-transmissive, such a sensor will have to be positioned ahead of the sealing station. An ejector downstream of the cutting station can then be actuated by a suitably delayed error signal from the sensor.
In many instances the molding station and the cutting station operate with different candences so that the carrier strip must intermittently advance through the mold in a mode different from that required for feeding the sealed tape to the cutter. Thus, an upstream transport roller pulling the carrier strip through the molding, filling and sealing stations will not rotate in synchronism with a downstream transport roller delivering the tape to the cutting station, even though the average rate of advance will be the same at all stations. The differences in instantaneous roller speeds can be taken into account by a loop of variable length formed by the tape between the two transporters; the presence of this loop, however, may on occasion lead to a phase shift between the operating cycles of the moding and cutting stations. If the machine is equipped with a monitoring device designed to detect improperly filled blisters ahead of the upstream transporter, an ejector responsive to an error signal from the monitoring device can eliminate the defective package from the output of the cutting stage only if that error signal is delayed by precisely the time required for a blister or a row of blisters to travel from the vicinity of the monitoring device to the location of the ejector. Any phase shift of the type referred to above would then result in a malfunction.